Comparison of Gastrointestinal Symptoms and Gastric Emptying Scintigraphy Between Postural Orthostatic Tachycardia Patients With and Without Small Fiber Neuropathy

Introduction: Autonomic dysfunction is common in patients with postural orthostatic tachycardia syndrome (POTS) and affects multiple systems, including the gastrointestinal (GI) tract. Various subtypes of POTS exist: autoimmune, hyperadrenergic, and neuropathic. While these subtypes share features of common autonomic symptoms; it remains unclear how symptom presentation amongst other affected systems, such as the GI tract, differ across subtypes. We aimed to compare gastrointestinal symptom presentation and gastric emptying scintigraphy (GES) between POTS patients with and without small fiber neuropathy (SFN). Methods: We conducted a retrospective case series of all POTS patients at our institution who underwent autonomic testing between 2013-2021. Patients were divided into those with SFN (abnormal QSART test) and those without SFN (normal QSART). Demographics, comorbidities, and reported GI symptoms were extracted. GES results were also extracted with percentage emptying at 60-minute intervals (4-hour study). Chi2 and glmnet testing were used to compare the groups. Results: 97 POTS patients (14 men), who underwent autonomic testing for SFN were included. Median age was 36 (21-67). Common comorbidities included hypermobile Ehlers Danlos Syndrome (44%), and chronic fatigue syndrome (22%). POTS patients with SFN were more likely to have nausea (75% vs 55%, p=0.03), poor oral intake (32% vs 9%, p=0.01), parenteral nutrition dependence (9% vs 0%, p=0.01), and early satiety (36% vs 18%, p=0.05) (Table). Most demographics and GI symptoms did not show significance as predictors for SFN. Of the 97 patients, a total of 33 underwent GES for evaluation of reported GI symptoms. The percentage of patients with delayed GES was numerically higher but not statistically significant in POTS patients with SFN (45% vs 23%, p=0.21). There were no significant differences in mean gastric emptying between groups (Table). Conclusion: Our data affirms the high prevalence of GI symptoms in patients with POTS independent of SFN. Patient with SFN were more likely to have upper GI symptoms of nausea, poor oral intake and early satiety despite similarities in GES. This suggests that symptoms may be due to sensory rather than motor dysfunction. While some GI symptoms were more common in those with SFN, there was a lack of predictability of symptoms and demographics for SFN. This suggests the need to have a high clinical suspicion for diagnosing SFN in patients with POTS whose GI symptoms do not respond to conventional therapy. Table 1. - Baseline Demographics and Gastrointestinal Symptom Presentation across POTS patients with and without SFN and Gastric Emptying Results Variable All (n=97) POTS with SFN (n=53) POTS w/o SFN (n=44) p-value Basic Demographics Age: Median (IQR) 36 (30-46) 37 (32-48) 35 (27-40) 0.12 Sex, n (%) 0.59 Female 83 (86) 45 (85) 39 (89) Male 14 (14) 8 (15) 5 (11) Race, n (%) 0.17 White 83 (86) 43 (81) 40 (91) Other 14 (14) 10 (19) 4 (9) Co-morbidities Hypermobile EDS 43 (44) 23 (43) 20 (45) 0.84 CSF Leak 19 (20) 13 (25) 6 (14) 0.18 Chronic Fatigue Syndrome 21 (22) 14 (26) 7 (16) 0.21 Fibromyalgia 15 (15) 9 (17) 6 (14) 0.27 Diabetes 2 (2) 1 (2) 1 (2) 0.89 Hypothyroidism 14 (14) 5 (9) 9 (20) 0.12 Chronic Narcotic Use 7 (7) 1 (2) 6 (14) 0.03 Gastrointestinal Symptoms Abdominal pain, n (%) 63 (65) 37 (70) 26 (59) 0.27 Bloating, n (%) 44 (45) 26 (49) 18 (41) 0.42 Nausea, n (%) 64 (66) 40 (75) 24 (55) 0.03 Vomiting, n (%) 28 (29) 19 (36) 9 (20) 0.10 Dyspepsia, n (%) 9 (9) 7 (13) 2 (5) 0.09 Constipation, n (%) 57 (59) 35 (66) 22 (50) 0.11 Diarrhea, n (%) 34 (35) 23 (43) 11 (25) 0.06 Early Satiety, n (%) 27 (28) 19 (36) 8 (18) 0.05 Dysphagia, n (%) 11 (11) 6 (11) 5 (11) 0.99 Weight Loss, n (%) 26 (27) 16 (30) 10 (23) 0.41 Poor oral intake, n (%) 21 (22) 17 (32) 4 (9) 0.01 Enteral nutrition dependence, n (%) 4 (4) 3 (6) 1 (2) 0.40 Parenteral nutrition dependence, n (%) 5 (5) 5 (9) 0 (0) 0.04 Gastric Emptying Delayed Gastric Emptying, n (%) 12 (36) 9 (45) 3 (23) 0.21 Percentage Emptying at Various Durations 60 minutes: Mean (SD) 32.1 (22.3) 28.9 (24.6) 37.0 (18.2) 0.35 120 minutes: Mean (SD) 57.3 (27.3) 53.3 (29.4) 62.5 (24.6) 0.37 180 minutes: Mean (SD) 74.3 (24.9) 68.7 (26.8) 83.3 (19.2) 0.15 240 minutes: Mean (SD) 85.8 (17.4) 84.1 (18.4) 88.2 (16.6) 0.55